Semiconductor storage device

ABSTRACT

A semiconductor storage device includes a first memory cell electrically connected to a first bit line and a first word line, a second memory cell electrically connected to a second bit line and the first word line, and a first circuit configured to supply voltages to the first word line. During a reading operation to read a page of memory cells including the first memory cell and the second memory cell, the first circuit supplies a first voltage to the first word line while the first memory cell is selected as a read target during a first time period, and supplies a second voltage greater than the first voltage to the first word line while the second memory cell is selected as a read target during a second time period that is different from the first time period, and directly thereafter, supplies the first voltage to the first word line.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/695,470, filed on Sep. 5, 2017, which is based upon and claims thebenefit of priority from Japanese Patent Application No. 2017-056335,filed Mar. 22, 2017, the entire contents of which are incorporatedherein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor storagedevice.

BACKGROUND

As semiconductor storage devices, there are known NAND flash memories.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a semiconductor storage deviceaccording to a first embodiment.

FIG. 2 is a diagram illustrating a memory cell array in thesemiconductor storage device according to the first embodiment.

FIG. 3 is a circuit diagram illustrating a block in the semiconductorstorage device according to the first embodiment.

FIG. 4 is a cross-sectional view illustrating the block in thesemiconductor storage device according to the first embodiment.

FIG. 5 depicts threshold distributions of a memory cell transistor inthe semiconductor storage device according to the first embodiment.

FIG. 6 is a diagram illustrating a row decoder, a voltage generationcircuit, and the memory cell array in the semiconductor storage deviceaccording to the first embodiment.

FIG. 7 is a timing chart illustrating various voltages during a readoperation in the semiconductor storage device according to the firstembodiment.

FIG. 8 is a diagram illustrating aspects of a read operation in thesemiconductor storage device according to the first embodiment.

FIG. 9 is a diagram illustrating aspects of a read operation in thesemiconductor storage device according to the first embodiment.

FIG. 10 is a diagram illustrating a first example of a command sequencein the semiconductor storage device according to the first embodiment.

FIG. 11 is a diagram illustrating a second example of a command sequencein the semiconductor storage device according to the first embodiment.

FIG. 12 is a timing chart illustrating various voltages of a readoperation in a semiconductor storage device according to a comparativeexample.

FIG. 13 is a timing chart illustrating various voltages during a readoperation in a semiconductor storage device according to a secondembodiment.

FIG. 14 is a diagram illustrating aspects of the read operation in thesemiconductor storage device according to the second embodiment.

FIG. 15 is a diagram illustrating aspects of the read operation in thesemiconductor storage device according to the second embodiment.

FIG. 16 is a timing chart illustrating various voltages of a readoperation in a semiconductor storage device according to a thirdembodiment.

FIG. 17 is a timing chart illustrating various voltages of a readoperation in a semiconductor storage device according to a fourthembodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a semiconductor storage deviceincludes a first memory cell electrically connected to a first bit lineand a first word line, a second memory cell electrically connected to asecond bit line and the first word line, and a first circuit configuredto supply voltages to the first word line. During a reading operation toread a page of memory cells including the first memory cell and thesecond memory cell, the first circuit supplies a first voltage to thefirst word line while the first memory cell is selected as a read targetduring a first time period, and supplies a second voltage greater thanthe first voltage to the first word line while the second memory cell isselected as a read target during a second time period that is differentfrom the first time period, and directly thereafter, supplies the firstvoltage to the first word line.

Embodiments will be described below with reference to the drawings.Throughout the drawings, the same reference numerals are given to thesame components or portions.

First Embodiment

A semiconductor storage device according to a first embodiment will bedescribed with reference to FIGS. 1 to 12. Hereinafter, a 3-dimensionalstacked NAND flash memory in which memory cells are stacked3-dimensionally on a semiconductor substrate will be described as anexample of a semiconductor storage device. In the following description,the term “connection” includes not only a case of a direct connectionbetween two components but also a case of connection between twocomponents via an arbitrary, interposed element or elements. As usedherein, a “first terminal of a transistor” indicates one of a source anda drain of a transistor and a “second terminal of the transistor”indicates the other of the source and the drain of the transistor. Also,a “control terminal of the transistor” refers to a gate of a transistor.

Configuration Example of First Embodiment

Hereinafter, an example configuration of the first embodiment will bedescribed with reference to FIGS. 1 to 6.

As illustrated in FIG. 1, a semiconductor storage device 100 includesplanes 10A and 10B, an input/output circuit 14, a logic control circuit15, a ready/busy control circuit 16, a register 17, a sequencer 18, anda voltage generation circuit 19.

The input/output circuit 14 transmits and receives signals IO (IO0 toIO7) to and from the outside (a host or a memory controller) of thesemiconductor storage device 100. The signals IO include commands,addresses, and data. The input/output circuit 14 transmits commands andaddresses from the outside to the register 17. The input/output circuit14 transmits write data from the outside to sense amplifiers 13 (13A and13B) and transmits read data from the sense amplifiers 13 to theoutside. The input/output circuit 14 transmits data strobe signals DQSand /DQS to the outside along with the read data. The read data is readin synchronization with the signals DQS and /DQS.

The logic control circuit 15 receives various control signals from theoutside (from an external source) and controls the input/output circuit14 and the sequencer 18. As control signals, a chip enable signal /CE, acommand latch enable signal CLE, an address latch enable signal ALE, awrite enable signal /WE, a read enable signal /RE, a write protectsignal /WP, and the data strobe signals DQS and /DQS can be used. Thesignal /CE enables the semiconductor storage device 100, which is asemiconductor chip or the like. The signals CLE and ALE notifies theinput/output circuit 14 that the signals IO are commands and addressesrespectively. The signal /WE instructs the input/output circuit 14 toinput the signals IO. The signal /RE instructs the input/output circuit14 to output the signals IO. The signal /WP sets the semiconductorstorage device 100 to a protection state, for example, when power istransitioning on and off. The signals DQS and /DQS are received alongwith the write data. The write data is written in synchronization withthe signals DQS and /DQS.

The ready/busy control circuit 16 transmits the signal /RB to notify anoutside controller or the like of the state of the semiconductor storagedevice 100. The signal /RB indicates whether the semiconductor storagedevice 100 is in a ready state (that is, a state in which a command canbe received from the outside) or a busy state (that is, a state in whicha command can not be received from the outside).

The register 17 retains commands and addresses supplied thereto. Theregister 17 transmits the addresses to the row decoders 12 (12A and 12B)and the sense amplifiers 13 (13A and 13B) and also transmits commands tothe sequencer 18. The register 17 also retains various tables used forcontrolling the sequences performed according to the commands.

The sequencer 18 receives the commands and refers to the various tablesretained in the register 17. Then, the sequencer controls the entiresemiconductor storage device 100 according to information provided inthe various tables.

The voltage generation circuit 19 includes various drivers. The voltagegeneration circuit 19 generates voltages necessary for operations suchas writing, reading, and erasing data under the control of the sequencer18. The voltage generation circuit 19 supplies generated voltages to therow decoders 12 and the sense amplifiers 13.

The plane 10A includes a memory cell array 11A, the row decoder 12A, andthe sense amplifier 13A. The plane 10B has substantially the sameconfiguration as plane 10A, and thus includes a memory cell array 11B,the row decoder 12B, and the sense amplifier 13B. In the following, thespecific description of plane 10B will generally be omitted and onlyaspects of plane 10A will be described as representative of plane 10B aswell.

The row decoder 12A receives a row address from the register 17 andselects a corresponding word line WL inside the memory cell array 11Abased on the row address. Then, the row decoder 12A supplies a voltagefrom the voltage generation circuit 19 to the selected word line WL.

The sense amplifier 13A reads data stored in a memory cell via a bitline BL inside the memory cell array 11A and likewise writes data to amemory cell via a bit line BL by supplying a voltage from the voltagegeneration circuit 19 to the bit line BL. The sense amplifier 13Aincludes a data latch (not separately illustrated). The data latchtemporarily stores the write data and read data. The sense amplifier 13Areceives a column address from the register 17 and outputs data from thedata latch to the input/output circuit 14 based on the column address.

As illustrated in FIG. 2, the memory cell array 11A includes a pluralityof blocks BLK (BLK0, BLK1, BLK2 . . . ) including nonvolatile memorycell transistors (which may also be referred to in some instances asmemory cells) associated with rows and columns. The block BLK includes,for example, four string units SU (SU0 to SU3). Each string unit SUincludes a plurality of NAND strings 35. Any number of blocks could beprovided in the memory cell array 11A and likewise any number of stringunits could be provided.

As illustrated in FIG. 3, the NAND string 35 includes n memory celltransistors MT (MT0 to MTn−1) and selection transistors ST1 and ST2. Thememory cell transistor MT includes a control gate and a charge storagelayer and retains data in a nonvolatile manner. The memory celltransistors MT are connected in series between a first terminal of theselection transistor ST1 and a first terminal of the selectiontransistor ST2.

Control terminals of the selection transistors ST1 of the string unitsSU0 to SU3 are connected to select gate lines SGD0 to SGD3. Thus, thecontrol terminals of the selection transistors ST2 of the string unitsSU0 to SU3 are connected in common to, for example, a select gate lineSGS, but may be connected to different select gate lines SGS0 to SGS3 ofthe string units. Control terminals of the memory cell transistors MT0to MTn−1 in the same block BLK are commonly connected to word lines WL0to WLn−1.

The second terminals of the selection transistors ST1 of the NANDstrings 35 at the same column inside the memory cell array 11A arecommonly connected to any bit line BL (BL0 to BLm−1). That is, the bitlines BL commonly connect the NAND strings 35 between the plurality ofblocks BLK. Further, the second terminals of the plurality of selectiontransistors ST2 are commonly connected to a source line SL.

That is, the string unit SU is an aggregate of the NAND strings 35connected to the different bit lines BL and connected to the same selectgate line SGD. The block BLK is an aggregate of the plurality of stringunits SU that commonly use the word lines WL. The memory cell array 11Ais an aggregate of the plurality of blocks BLK that commonly use the bitlines BL.

Data is written or read en bloc on or from the memory cells MT connectedto any of word lines WL inside the string unit SU. The unit of wordlines is referred to as pages.

On the other hand, erasing of data can be performed in units of blocksBLK or units smaller than the block BLK. An erasing method is disclosedin, for example, U.S. patent application Ser. No. 13/235,389, a“NONVOLATILE SEMICONDUCTOR MEMORY DEVICE,” filed on Sep. 18, 2011. Anerasing method is also disclosed in U.S. patent application Ser. No.12/694,690, a “NONVOLATILE SEMICONDUCTOR STORAGE DEVICE,” filed on Jan.27, 2010. An erasing method is also disclosed in U.S. patent applicationSer. No. 13/483,610, “NONVOLATILE SEMICONDUCTOR MEMORY DEVICE AND DATAERASE METHOD THEREOF,” filed on May 30, 2012, the entire contents offoregoing list of patent applications are incorporated herein byreference.

As illustrated in FIG. 4, the plurality of NAND strings 35 are providedon a p-type well region 20, which may be a region of a semiconductorsubstrate. For example, four wiring layers 21, functioning as selectgate lines SGS, n-number of wiring layers 22, functioning as word linesWL (e.g., WL0 to WLn−1), and four wiring layers 23, functioning asselect gate lines SGD, are sequentially stacked on the well region 20.Insulating layers (not specifically illustrated) are formed betweenthese stacked wiring layers.

Pillar-like (column-like) conductors 24 passing through these wiringlayers 21, 22, and 23 and reaching the well region 20 are provided. Agate insulation layer 25, a charge storage layer (which can be aninsulating layer or a conductive layer) 26, and a block insulating layer27 are sequentially provided on a side surface of the conductor 24. Theconductor 24, the gate insulation layer 25, the charge storage layer 26,and the block insulating layer 27 configure the memory cell transistorMT and the selection transistors ST1 and ST2. Each conductor 24functions as a current path of a NAND string 35 and is a region in whicha channel of each transistor is formed. The upper end of the conductor24 is connected to a metal wiring layer 28 that functions as a bit lineBL.

An n⁺ type impurity diffusion layer 29 is provided inside a region atthe surface of the well region 20. A contact plug 30 is provided on thediffusion layer 29. The contact plug 30 is connected to a metal wiringlayer 31 that functions as a source line SL. Further, a p⁺ type impuritydiffusion layer 32 is provided in a region at the surface of the wellregion 20. A contact plug 33 is provided on the diffusion layer 32. Thecontact plug 33 is connected to a metal wiring layer 34 that functionsas a well wiring CPWELL. The well wiring CPWELL is a wiring for applyinga potential to the conductor 24 via the well region 20.

A plurality of the foregoing described configurations are arrayed alonga direction (referred to as a “depth direction”) into the page of FIG.4. The string unit SU includes a set of NAND strings 35 arranged in thedepth direction.

Furthermore, another configuration may be used as the configuration ofthe memory cell array 11A. For example, the configuration of the memorycell array 11A may be as disclosed in U.S. patent application Ser. No.12/407,403, “THREE DIMENSIONAL STACKED NONVOLATILE SEMICONDUCTORMEMORY,” filed on Mar. 19, 2009. Or the configuration of the memory cellarray 11A can be as disclosed in U.S. patent application Ser. No.12/406,524, “THREE DIMENSIONAL STACKED NONVOLATILE SEMICONDUCTORMEMORY,” filed on Mar. 18, 2009; U.S. patent application Ser. No.12/679,991, “NONVOLATILE SEMICONDUCTOR STORAGE DEVICE AND METHOD OFMANUFACTURING THE SAME,” filed on Mar. 25, 2010; or U.S. patentapplication Ser. No. 12/532,030, “SEMICONDUCTOR MEMORY AND METHOD FORMANUFACTURING SAME” filed on Mar. 23, 2009, the entire contents each ofwhich are incorporated herein by reference.

FIG. 5 illustrates an example in which the memory cell transistor MTstores 2-bit (4-value) data.

As illustrated in FIG. 5, a threshold voltage of the memory celltransistor MT can be written to have a value included in one of fourdiscrete distributions. These four distributions are referred to as anEr level, an A level, a B level, and a C level in this order from lowerto higher thresholds.

The Er level is equivalent to, for example, a data erase state. Thethreshold voltages included in the Er level are less than a verificationvoltage VFYA and can have a positive or negative voltage value.

The A to C levels are states in which charges have been injected to acharge storage layer and data has been specifically written to thememory cell. The thresholds included in the distributions of the A to Clevels have, for example, positive values. The threshold voltagesincluded in the A level are equal to or greater than the verificationvoltage VFYA and less than a verification voltage VFYB. The thresholdvoltages included in the B level are equal to or greater than theverification voltage VFYB and are less than a verification voltage VFYC.The threshold voltages included in the C level are equal to or greaterthan the verification voltage VFYC and are less than a read pass voltageVREAD. In general, a relationship of VFYA<VFYB<VFYC<VREAD is satisfied.

A read voltage VA is set to be between the Er level and the A level, aread voltage VB is set to be between the A level and the B level, and aread voltage VC is set to be between the B level and the C level. Theread voltage relationship, in general, satisfies the following: VA<VFYA,VB<VFYB, and VC<VFYC. The memory cell transistors MT to which the readvoltages VA, VB, and VC are applied are turned on or off in accordancewith the stored data therein, and it can be determined whether thethreshold voltages of the memory cell transistors are greater or lessthan the applied read voltages. The read pass voltage VREAD is a voltagegreater than an upper limit of the highest threshold voltagedistribution (here, the C level) and the memory cell transistor MT towhich the read pass voltage VREAD is applied is turned on regardless ofthe stored data therein.

As described above, each memory cell transistor MT can have any of thefour threshold distributions and can take any of four kinds of differentstates. By allocating to these each of these four different possiblestates a binary notation value (“00” to “11”), each memory celltransistor MT can be operated to retain 2-bit data.

Embodiments can also be applied to memory cell transistors MT capable ofstoring data of 3 bits or more. Similarly, embodiments can be applied tomemory cell transistors MT capable of storing only 1-bit data.

In FIG. 6, the row decoder 12A and the voltage generation circuit 19 areillustrated.

As illustrated in FIG. 6, the row decoder 12A includes transmissiontransistors 51, 52 (52_0 to 52_n−1 corresponding to the word lines WL),and 53 and a block decoder 54.

In the transmission transistor 51, a first terminal is electricallyconnected to a wiring SGSD and a second terminal is electricallyconnected to the select gate line SGS. In the transmission transistors52_0 to 52_n−1, first terminals are electrically connected to the wordlines WL0 to WLn−1 and second terminals are electrically connected tocontrol gate lines CG0 to CGn−1. In the transmission transistor 53, afirst terminal is electrically connected to a wiring SGDD and a secondterminal is electrically connected to a select gate line SGD. Signalsfrom the block decoder 54 are supplied to control terminals of thetransmission transistors 51, 52, and 53.

The block decoder 54 decodes block addresses. The block decoder 54supplies signals (voltages) to the control terminals of the transmissiontransistors 51, 52, and 53 for turning on or off the transmissiontransistors 51, 52, and 53 according to decoding results of the blockaddresses. More specifically, when corresponding blocks are selected,the block decoder 54 supplies voltages for turning on the transmissiontransistors 51, 52, and 53. Conversely, when the corresponding blocksare not selected, the block decoder 54 supplies voltages for turning offthe transmission transistors 51, 52, and 53. Here, a state in which thetransistors are turned on refers to a state in which the transistortransmits an applied voltage from the first terminal to the secondterminal.

The voltage generation circuit 19 includes an SGS driver 41, CG drivers42 (42_0 to 42_n−1), and an SGD driver 43.

The SGS driver 41 generates a voltage necessary on the select gate lineSGS and supplies the voltage to the wiring SGSD during variousoperations. The transmission transistor 51 transmits a voltage from theSGS driver 41 to the select gate line SGS under the control of the blockdecoder 54.

The CG drivers 42_0 to 42_n−1 generate voltages necessary on the wordlines WL0 to WLn−1 and supply these voltages to the control gate linesCG0 to CGn−1 during various operations. The transmission transistors52_0 to 52_n−1 transmit the voltages from the CG drivers 42_0 to 42_n−1to the word lines WL0 to WLn−1 under the control of the block decoder54.

The SGD driver 43 generates a voltage necessary on the select gate lineSGD and supplies the voltage to the wiring SGDD during variousoperations. The transmission transistor 53 transmits the voltage fromthe SGD driver 43 to the select gate line SGD under the control of theblock decoder 54.

Read Operation of First Embodiment

Hereinafter, a read (reading) operation according to the firstembodiment will be described with reference to FIGS. 7 to 9. FIG. 7 is atiming chart illustrating various voltages at the time of selectingcolumns of a first region and the time of selecting columns of a secondregion in a read operation. FIG. is a diagram illustrating the voltagesat the time of selecting columns of the first region in the readoperation and FIG. 9 is a diagram illustrating the voltages at the timeof selecting the columns of the second region in the read operation.

As illustrated in FIGS. 7 to 9, in this example, the memory cell array11A can be considered to be divided into two regions (e.g., the firstand second regions) according to column units (units of bit lines BL)and the read operation can be performed in each region separately. Thefirst and second regions boundaries are set here according to distancesfrom the voltage generation circuit 19 (a CG driver 42). Morespecifically, the first region is the region generally closer to the CGdriver 42 and the second region is the region generally more distantfrom the CG driver 42. Here, an example is illustrated in which thereare bit lines BL0 to BL15 provided in the memory cell array 11A, thefirst region is set to include the bit lines BL0 to BL7, and the secondregion is set to include the bit lines BL8 to BL15. The voltages to besupplied to the selected word lines WL during the reading operation arecontrolled and set separately for selection of the columns in the firstregion and selection of the columns in the second region.

First, a timing chart in the case of the selection of the columns (thebit lines BL0 to BL7) in the first region during a reading operationwill be described with reference to FIGS. 7 and 8.

In FIG. 7, “Sel.WL” indicates a selected word line, “Unsel.WL” indicatesa non-selected word line, “Sel.BL” indicates a selected bit line, and“Unsel.BL” indicates a non-selected bit line. The solid line in timingchart for the selected word line WL (the “Sel.WL” row) indicates avoltage waveform for a portion of the selected word line WL close to(physical proximity) the CG driver 42 (for example, a portion of aselected word line located in the first region and this close-in wordline portion is referred to as a “first portion” in description below).This solid line for Sel.WL is substantially the same as the voltagesupplied from the CG driver 42. On the other hand, a dotted line in thetiming cart of the selected word line WL (the “Sel.WL” rows) depicts thevoltage waveform for a portion of the selected word line WL relativelydistant from the CG driver 42 (for example, a portion of the selectedword line WL located in the second region and this distant word lineportion is referred to as a “second portion” in description below). Thedifference in solid and dotted line values for the selected word line isbecause the voltage from the CG driver 42 is delayed and applieddepending on the distance of the word line WL portion from the CG driver42. Here, an example in which the word line WL0 has been selected isillustrated. FIG. 7 illustrates an example in which reading using thevoltage VA and reading using the voltage VC are sequentially performed.

As illustrated in FIGS. 7 and 8, the various voltages depicted are at avoltage level VSS during an initial state (the time before time T11).

Then, at time T11, the CG drivers 42_1 to 42_n−1 supply the voltageVREAD to non-selected word lines WL1 to WLn−1. Accordingly, the memorycell transistors MT1 to MTn−1 connected to the non-selected word linesWL1 to WLn−1 are turned on regardless of the threshold.

At time T11, the SGS driver 41 supplies the voltage VSG to the selectgate line SGS and the SGD driver 43 supplies the voltage VSG to theselect gate line SGD. The voltage VSG is a voltage for turning on theselection transistors ST1 and ST2.

At time T11, a voltage VBL (which is less than VREAD) is applied to theselected bit lines BL0 to BL7 and a voltage VSRC (which is less thanVBL) is applied to the non-selected bit lines BL8 to BL15.

At time T11, the CG driver 42_0 supplies the voltage VA to the selectedword line WL0. Thus, the voltage VA is applied to the first portion ofthe selected word line WL0. Thus, reading is performed in accordancewith the voltage VA of the memory cell transistor MT0 connected to theselected word line WL0 and connected to the selected bit lines BL0 toBL7 (located in the first region).

A voltage less than the voltage VA is, in effect, applied to or receivedby the second portion of the selected word line WL0. In other words, thesecond portion of the selected word line WL0 does not reach the voltageVA necessary for the reading (does not reach to the voltage VA) due tolong-distance between the voltage application spot on the selected wordline WL0 and the second portion. However, in this embodiment, thecolumns of the second region in which the second portion of the selectedword line WL0 is located are non-selected. Therefore, reading of thememory cell transistor MT0 connected to the selected word line WL0 andconnected to the selected bit lines BL8 to BL15 (located in the secondregion) is not necessary. Accordingly, there is no reading error in theread operation in this example.

Subsequently, at time T13, the CG driver 42_0 supplies the voltage VC tothe selected word line WL0. Thus, the voltage VC is applied to the firstportion of the selected word line WL0. Then, reading is performed inaccordance with the voltage VC of the memory cell transistor MT0connected to the selected word line WL0 and connected to the selectedbit lines BL0 to BL7 (located in the first region).

At this time, a voltage less than the voltage VC is, in effect, appliedto or received by the second portion of the selected word line WL0. Inother words, the second portion of the selected word line WL0 does notreach the voltage VC necessary for the reading operation due to thelong-distance. However, as was the case at the time of the reading atvoltage VA level, no problem occurs in the read operation in thisexample because the second region bit lines BL are unselected.

Thereafter, at time T15, the various voltages begin to return to thevoltage VSS. Thus, each transistor is turned off and the read operationends.

Next, a timing chart in the case of selection of the columns (the bitlines BL8 to BL15) of the second region in a read operation will bedescribed with reference to FIGS. 7 and 9.

As illustrated in FIGS. 7 and 9, the various depicted voltages are thevoltage VSS in an initial state (e.g., before time T11).

At time T11, as was the case in which the columns of the first regionwere selected, the voltage VREAD is applied to the non-selected wordlines WL1 to WLn−1, the voltage VSG is applied to the select gate lineSGS, and the voltage VSG is applied to the select gate line SGD. At timeT11, the voltage VBL is applied to the selected bit lines BL8 to BL15and the voltage VSRC is applied to the non-selected bit lines BL0 toBL7.

Further, at time T11, the CG driver 42_0 supplies a voltage VK1 to theselected word line WL0. Thus, the voltage VK1 is applied to the firstportion of the selected word line WL0. The voltage VK1 is a relativelylarge voltage that is temporarily supplied by the CG driver 42_0 and therelation of VK1>VA is satisfied. In accordance with the voltage VK1, thevoltage VA is applied to the second portion of the selected word lineWL0 without substantial delay (that is, at timing faster than when onlythe voltage VA is supplied by the CG driver 42_0 to the first portion).

Thereafter, at time T12, the CG driver 42_0 supplies the voltage VA tothe selected word line WL0. Thus, the voltage VA is applied to the firstportion of the selected word line WL0 at this time. Then, reading isperformed in accordance with the nominal voltage VA level of the memorycell transistor MT0 connected to the selected word line WL0 andconnected to the selected bit lines BL8 to BL15 (located in the secondregion).

At this time, the voltage VA is applied to the first portion of theselected word line WL0 after the voltage VK1 is applied. Therefore, inthe first portion of the selected word line WL0, it takes some timeuntil voltage stabilization at the voltage VA necessary for the readingoccurs. However, the columns of the first region in which the firstportion of the selected word line WL0 is located are non-selected.Therefore, reading of the memory cell transistor MT0 connected to theselected word line WL0 and connected to the selected bit lines BL0 toBL7 (located in the first region) is not necessary. Accordingly, aproblem does not occur in the read operation in this example.

Subsequently, at time T13, the CG driver 42_0 supplies the voltage VK2to the selected word line WL0. Thus, the voltage VK2 is applied to thefirst portion of the selected word line WL0. The voltage VK2 is arelatively large voltage temporarily supplied by the CG driver 42_0 anda relationship of VK2>VC is satisfied. In accordance with the voltageVK2 being applied to the first portion of the selected word line WL0,the voltage VC is applied to the second portion of the selected wordline WL0 without delay (that is, faster than when just voltage VC issupplied to the first portion).

Thereafter, at time T14, the CG driver 42_0 supplies the voltage VC tothe selected word line WL0. Thus, the voltage VC is applied to the firstportion of the selected word line WL0. Then, reading is performed inaccordance with the voltage VC on the memory cell transistor MT0connected to the selected word line WL0 and connected to the selectedbit lines BL8 to BL15 (located in the second region).

At this time, the voltage VC is applied to the first portion of theselected word line WL0 after the voltage VK2 has been applied.Therefore, it takes some time until stabilization at the voltage VClevel necessary for the reading to occur in the first portion of theselected word line WL0. However, as was the case at the time of readingin accordance with the voltage VA, a problem does not occur in the readoperation in this example.

Thereafter, at time T15, the various voltages return to voltage VSS.Thus, each transistor is turned off and the read operation ends.

Even when the columns of the first region are being selected, the CGdriver 42_0 may supply the temporarily large voltages VK1′ and VK2′ tothe selected word line WL0 at time T11 and time T13, respectively. Here,a relationship of VK1′ <VK1 and a relationship of VK2′<VK2 aresatisfied.

Command Sequence of First Embodiment

In the above-described read operation, eight bit lines BL, for example,are set as read units and eight bit lines BL in one of the first orsecond region are selected. When the first region is selected, thevoltages VA and VC are supplied in sequence to the selected word linesWL. Conversely, when the second region is selected, the voltages VK1,VA, VK2, and VC are supplied in sequence to the selected word lines WL.The setting of a special read mode, that is, the setting of the readunits and the selection of the read region, comply with a receivedcommand.

Hereinafter, a command sequence by which the read operation is performedwill be described with reference to FIGS. 10 and 11. In the followingdescription, a command, an address, and data are issued from the outside(e.g., a memory controller or the like) and are received by thesemiconductor storage device 100. The command, the address, and the dataare input in synchronization with assertion of each signal.

A first example illustrated in FIG. 10 is an example in accordance witha special command sequence.

As illustrated in FIG. 10, in the first example, the semiconductorstorage device 100 first receives a command CMD1. The command CMD1 is aspecial command and is a command for selecting the special read mode.Here, the command CMD1 is a command for setting the read units. Morespecifically, the command CMD1 is used to set eight bit lines BL as theread units.

Subsequently, the semiconductor storage device 100 receives an addressADD1. The address ADD1 is an address for designating a region in whichdata is to be read in the special reading by the command CMD1. Morespecially, the address ADD1 can be an address for designating, forexample, the plane 10A and the first region.

The special read mode is set in accordance with the command CMD1 and theaddress ADD1. That is, by the setting of the read units and theselection of the read region as in the above example a reading operationis performed and voltages to be supplied to the selected word lines WLare determined according to the selected read region being the first orsecond region.

Subsequently, the semiconductor storage device 100 receives acommand/address (CA) set. The CA set is normally a set of a command andan address necessary to perform the reading.

More specifically, the semiconductor storage device 100 first receives acommand CMD2. The command CMD2 is a command for ordering to input anaddress in reading. Subsequently, the semiconductor storage device 100receives addresses ADD (ADD2 to ADD6) over the course of, for example,five cycles. The addresses ADD2 to ADD6 are addresses for designatingaddresses for reading data and are used to designate, for example, ablock, a partial block (string units), a row (word line), and columns(bit lines). More specifically, for example, the block BLK0, the stringunit SU0, the word line WL0, and the bit lines BL0 to BL7 can beselected. The number of selected bit lines BL0 to BL7 is based on asetting by the above-described command CMD1. Thereafter, thesemiconductor storage device 100 receives a command CMD3. The commandCMD3 is a command for ordering performance of the reading.

The semiconductor storage device 100 enters a busy state (RB=“L” level)and starts the reading in response to the command CMD3. During a periodt1, which is the busy state, the reading is performed. Here, eight bitlines BL are set as read units and the first region is read.Accordingly, the voltages VA and VC are supplied in sequence to theselected word lines WL. Thereafter, the semiconductor storage device 100enters a ready state (RB=“H” level) and ends the reading.

A second example illustrated in FIG. 11 is an example in accordance witha set feature command sequence.

As illustrated in FIG. 11, in the second example, the semiconductorstorage device 100 first receives a command CMD4. The command CMD4 is acommand for ordering a change in parameters in the semiconductor storagedevice 100.

Subsequently, the semiconductor storage device 100 receives an addressADD7. The address ADD7 is an address for designating an addresscorresponding to a parameter desired to be changed. Here, the changedparameter is the read mode setting.

Subsequently, the semiconductor storage device 100 receives data DT (DT1to DT4) over, for example, four cycles. The data DT is data equivalentto parameters to be changed. Here, the data DT includes, for example,the read units, the read regions, and the voltages to be supplied to theselected word lines WL.

Thus, the semiconductor storage device 100 enters a busy state andstarts set feature. During a period t2, which is the busy state, the setfeature is performed and the set parameters can be rewritten.

In this way, the special read mode is set in accordance with the commandCMD4, the address ADD7, and the data DT. That is, the setting of theread units and the selection of the read region in this example areperformed and voltages to be supplied to the selected word lines WL aredetermined according to the selected read region by adjusting values ofread operation set parameters.

When the set feature ends, the semiconductor storage device 100 is setto the special read mode. Accordingly, when the command/address (CA) setis received, the semiconductor storage device 100 enters the busy stateand starts the reading. During a period t3, which is a busy state, thesame reading as the reading during the period t1 in FIG. 10 isperformed.

Advantages of First Embodiment

As illustrated in FIG. 12, in a comparative example, all of the columns(the bit lines BL0 to BL15) are selected and the read operation isperformed. The voltages VK1, VA, VK2, and VC are supplied in sequence tothe selected word lines WL. That is, in the comparative example, at timeT21 to time T25, all of the bit lines BL0 to BL15 are selected andvoltages in the case of the selection of the second region in theforegoing first embodiment are supplied to the selected word lines WL.

At this time, by supplying the voltages VK1 and VK2 to the selected wordlines WL, the second portion (the portion distant from the CG driver 42)of the selected word lines WL can be boosted to the voltages VA and VCrapidly. However, the first portion (the portion close to the CG driver)of the selected word lines WL is also boosted to the voltages VK1 andVK2. Therefore, it takes some time until the first portion drops to theappropriate voltages VA and VC for reading. As a result, in particular,it takes some additional time to read the memory cell transistors MT onthe first portion side of the selected word lines WL since reading ofthe first portion must wait until the voltage stabilizes at theappropriate level VA or VC. A large voltage is applied temporarily tothe first portion of the selected word lines WL and the memory celltransistors MT on the first portion side can be turned on in some cases.Thus, noise occurs from the word lines WL to the bit lines BL in somecases, a delay time is necessary for the bit lines BL to be stabilized,and thus it takes further additional time to perform reading in thecomparative example.

In the first embodiment, however, the memory cell array 11A isconceptually divided into the first region (the region close to the CGdriver 42) and the second region (the region distant from the CG driver42) as groups/units of columns (bit lines BL) and the read operation isseparately performed in each region. The voltages to be supplied to theselected word lines WL are appropriately controlled for the case ofselection of the columns of the first region and for the case ofselection of the columns of the second region. Thus, the read voltages(VA and VC) can be applied rapidly to the first or second portion of theselected word lines WL, and thus it is possible to achieve a shorteningof the read time.

More specifically, as illustrated in FIG. 7, when the columns of thefirst region are selected, the voltages VA and VC are supplied insequence to the selected word lines WL. Thus, the voltages of the firstportion of the selected word lines WL can be boosted to the voltages VAand VC rapidly and stabilized, and thus it is possible to achieve theshortening of the read time. On the other hand, the second portion ofthe selected word lines WL does not reach the voltages VA and VCnecessary for the reading during the reading of the first region.However, since the columns of the second region in which the secondportion of the selected word lines WL are located are non-selected, thereading of the memory cell transistors MT in the second region is notnecessary. Accordingly, a problem does not occur in the read operation.

As illustrated in FIG. 7, when the columns of the second region areselected, the voltages VK1, VA, VK2, and VC are supplied in sequence tothe selected word lines WL. Thus, the voltages of the second portion ofthe selected word lines WL can be boosted to the voltages VA and VCrapidly to be stabilized, and thus it is possible to achieve theshortening of the read time. However, as noted above, it takes some timeuntil the first portion of the selected word lines WL to be stabilizedin accordance with the voltages VA and VC necessary for the reading.However, since the columns of the first region in which the firstportion of the selected word lines WL are located are non-selected, thereading of the memory cell transistor MT in the first region is notnecessary in this read operation at this time. Accordingly, a problemdoes not occur in the read operation in this example.

When the columns of the second region in the first embodiment areselected, the voltages VK1 and VK2 can generally be set to be greaterthan those of the comparative example. Thus, it is possible to boost thevoltage of the second portion of the selected word lines WL to theappropriate read voltages VA and VC more rapidly.

In the first embodiment, the memory cell array 11 in the plane 10 isdivided into two regions, the first and second regions, but the presentdisclosure is not limited thereto. The memory cell array 11 may also bedivided into three regions or more.

In the first embodiment, a 3-dimensional stacked NAND flash memory hasbeen described as a semiconductor storage device as one example, but thepresent disclosure is not limited to this example. The presentdisclosure can also be applied to a two-dimensionally arrayed NAND flashmemory.

Second Embodiment

A semiconductor storage device according to a second embodiment will bedescribed with reference to FIGS. 13 to 15. In the second embodiment,reading using a bit line shield scheme is performed. The bit line shieldscheme is a scheme of selecting, for example, only odd columns or evencolumns during a reading process, then reading the other columns inanother reading process.

In the second embodiment, points of difference from the first embodimentwill be mainly described and repeated aspects will not be describedagain.

Read Operation of Second Embodiment

Hereinafter, a read operation according to the second embodiment will bedescribed with reference to FIGS. 13 to 15.

FIG. 13 is a timing chart illustrating various voltages at the time ofselecting odd columns of a first region and the time of selecting oddcolumns of a second region in a read operation. FIG. 14 is a diagramillustrating the voltages at the time of selecting odd columns of thefirst region in the read operation and FIG. 15 is a diagram illustratingthe voltages at the time of selecting the odd columns of the secondregion in the read operation.

As illustrated in FIGS. 13 to 15, in this example, the memory cell array11A is divided into two regions (first and second regions) in units ofcolumns (units of bit lines BL) and each region is further divided intoodd columns and even columns. Voltages to be supplied to the selectedword lines WL are appropriately controlled for the case of selection ofthe columns (e.g., the odd columns or the even columns) in the firstregion and for the case of selection of the columns (e.g., the oddcolumns and the even columns) in the second region.

The control for selection of the even columns of each region issubstantially the same as the control for selection of the odd columns.Therefore, a case in which the odd columns are selected will bedescribed below as representative of both odd and even column reading.

First, a timing chart in the case of selection of the odd columns (thebit lines BL1, BL3, BL5, and BL7) of the first region in the readoperation will be described with reference to FIGS. 13 and 14.

As illustrated in FIGS. 13 and 14, at time T31 to time T35, the voltagesVA and VC are applied in sequence to the selected word line WL0 as inthe first embodiment. As in the first embodiment, the voltage VREAD isapplied to the non-selected word lines WL1 to WLn−1, the voltage VSG isapplied to the select gate line SGS, and the voltage VSG is applied tothe select gate line SGD.

On the other hand, at time T31 to T35, the voltage VBL is applied to theselected bit lines BL1, BL3, BL5, and BL7 and the voltage VSRC isapplied to the non-selected bit lines BL0, BL2, BL4, BL6, and BL8 toBL15, unlike the first embodiment.

Thus, the reading is performed in accordance with the voltages VA and VCof the memory cell transistor MT0 connected to the selected word lineWL0 and connected to the selected bit lines BL1, BL3, BL5, and BL7.Conversely, the reading is not performed in accordance with the voltagesVA and VC of the memory cell transistor MT0 connected to the selectedword line WL0 and connected to the non-selected bit lines BL0, BL2, BL4,BL6, and BL8 to BL15.

At this time, the non-selected bit lines BL0, BL2, BL4, and BL6 in thefirst region function as shield lines. That is, the non-selected bitlines BL0, BL2, BL4, and BL6 in the first region reduce noise during theread operation of the selected bit lines BL1, BL3, BL5, and BL7 in thefirst region.

Next, a timing chart in the case of selection of the odd columns (thebit lines BL9, BL11, BL13, and BL15) of the first region in the readoperation will be described with reference to FIGS. 13 and 15.

As illustrated in FIGS. 13 and 15, at time T31 to time T35, the voltagesVK1, VA, VK2, and VC are applied in order to the selected word line WL0,as in the first embodiment. As in the first embodiment, the voltage VRADis applied to the non-selected word lines WL1 to WLn−1, the voltage VSGis applied to the select gate line SGS, and the voltage VSG is appliedto the select gate line SGD.

Conversely, at time T31 to time T35, the voltage VBL is applied to theselected bit lines BL9, BL11, BL13, and BL15 and the voltage VSRC isapplied to the non-selected bit lines BL0 to BL7, BL8, BL10, BL12, andBL14, unlike the first embodiment.

Thus, the reading is performed in accordance with the voltages VA and VCof the memory cell transistor MT0 connected to the selected word lineWL0 and connected to the selected bit lines BL9, BL11, BL13, and BL15.Conversely, the reading is not performed in accordance with the voltagesVA and VC of the memory cell transistor MT0 connected to the selectedword line WL0 and connected to the non-selected bit lines BL0 to BL7,BL8, BL10, BL12, and BL14.

At this time, the non-selected bit lines BL8, BL10, BL12, and BL14 inthe second region function as shield lines. That is, the non-selectedbit lines BL9, BL11, BL13, and BL15 in the first region reduce noise atthe time of the read operation of the selected bit lines BL8, BL10,BL12, and BL14 in the first region.

Advantages of Second Embodiment

In the second embodiment, each of the first and second regions isfurther divided into the odd columns and the even columns. Thus, thenon-selected bit lines BL (for example, the even bit lines BL) functionas the shield lines with respect to the selected bit lines BL (forexample, the odd bit lines BL). Accordingly, the noise on the selectedbit lines BL at the time of the read operation is reduced and thevoltages of the selected bit lines BL can be stabilized rapidly. Thus,it is possible to achieve a shortening of the read time.

Third Embodiment

A semiconductor storage device according to a third embodiment will bedescribed with reference to FIG. 16. In the third embodiment, a refreshoperation is performed initially in a read operation. In the thirdembodiment, voltages to be supplied at the time of charging of theselected word lines WL described in the foregoing first embodiment andalso at the time of discharging of the selected word lines WL after arefresh operation are appropriately controlled.

In the third embodiment, differences from the first embodiment will bemainly described and similarities and repeated aspects will not bedescribed.

Read Operation of Third Embodiment

Hereinafter, a read operation according to the third embodiment will bedescribed with reference to FIG. 16. FIG. 16 is a timing chartillustrating various voltages at the time of selecting columns of thefirst region and the time of selecting columns of the second region in aread operation.

As illustrated in FIG. 16, the memory cell array 11A is conceptuallydivided into two regions in column units and the read operation isperformed in each region. At this time, a refresh operation is performedat the beginning of the read operation. The refresh operation is anoperation for removing charges remaining inside the conductors 24 at thestart of various operations in a 3-dimensional stacked NAND flashmemory. Voltages to be supplied to the selected word lines WL arecontrolled according to the selection of the columns of the first regionand the selection of the columns of the second region.

First, the timing chart in the case of selection of the columns (the bitlines BL0 to BL7) of the first region in the read operation will bedescribed with reference to FIG. 16. FIG. 16 illustrates an example inwhich reading in accordance with the voltage VA and reading inaccordance with the voltage VC are successively performed after therefresh operation has been performed.

As illustrated in FIG. 16, the various voltages are voltage VSS in aninitial state (before time T41).

Then, at time T41, the CG drivers 42_1 to 42_n−1 supply the voltageVREAD to non-selected word lines WL1 to WLn−1. Accordingly, the memorycell transistors MT1 to MTn−1 connected to the non-selected word linesWL1 to WLn−1 are turned on regardless of threshold.

Subsequently, at time T41, the CG driver 42_0 also supplies the voltageVREAD to the non-selected word line WL0. Thus, the memory celltransistor MT0 connected to the non-selected word line WL0 is turned onregardless of its threshold.

At time T41, the SGS driver 41 supplies the voltage VSG to the selectgate line SGS and the SGD driver 43 supplies the voltage VSG to theselect gate line SGD. Thus, the selection transistors ST1 and ST2 areturned on.

At time 141, the voltage VBL is applied to the selected bit lines BL0 toBL7 and the voltage VSRC is applied to the non-selected bit lines BL8 toBL15.

Thus, the refresh operation is performed. That is, a refresh currentflows to all the memory strings 36 and charges remaining in theconductors 24 (channels) are removed.

Next, at time T42, the CG driver 42_0 supplies the voltage VA to theselected word line WL0. Thus, the voltage VA is applied to the firstportion of the selected word line WL0. Thus, reading is performed inaccordance with the voltage VA of the memory cell transistor MT0connected to the selected word line WL0 and connected to the selectedbit lines BL0 to BL7 (located in the first region).

At this time, a voltage greater than the voltage VA is, in effect,applied to the second portion of the selected word line WL0. In otherwords, the second portion of the selected word line WL0 does not reachthe voltage VA necessary for the reading due to long-distance delay.However, since the columns of the second region in which the secondportion of the selected word line WL0 is located are non-selected, aproblem does not occur in the read operation in this example.

Subsequently, at time 144, the CG driver 42_0 supplies the voltage VC tothe selected word line WL0. Thus, the voltage VC is applied to the firstportion of the selected word line WL0. Then, reading is performed inaccordance with the voltage VC of the memory cell transistor MT0connected to the selected word line WL0 and connected to the selectedbit lines BL0 to BL7 (located in the first region).

At this time, a voltage less than the voltage VC is, in effect, appliedto the second portion of the selected word line WL0. In other words, thesecond portion of the selected word line WL0 does not reach the voltageVC necessary for the reading (does not boost to the voltage VC) due tolong-distance delay. However, as was the case at the time of the readingin accordance with the voltage VA, a problem does not occur in the readoperation in this example.

Thereafter, at time T46, the various voltages are returned to voltageVSS. Thus, each transistor is turned off and the read operation ends.

Next, a timing chart in the case of selection of the columns (the bitlines BL8 to BL15) of the second region in the read operation will bedescribed with reference to FIG. 16.

As illustrated in FIG. 16, various voltages are voltages VSS in aninitial state (before time T41).

At time T41 to time T42, the refresh operation is performed as was alsothe case of selection of the columns of the first region.

Subsequently, at time T42, the CG driver 42_0 supplies a voltage VK3 tothe selected word line WL0. Thus, the voltage VK3 is applied to thefirst portion of the selected word line WL0. The voltage VK3 is a lowervoltage temporarily supplied by the CG driver 42_0 and a relation ofVK3<VA is satisfied. In accordance with the voltage VK3, the voltage VAis applied to the second portion of the selected word line WL0 withoutdelay (faster than when VA is supplied).

Thereafter, at time T43, the CG driver 42_0 supplies the voltage VA tothe selected word line WL0. Thus, the voltage VA is applied to the firstportion of the selected word line WL0. Then, reading is performed inaccordance with the voltage VA of the memory cell transistor MT0connected to the selected word line WL0 and connected to the selectedbit lines BL8 to BL15 (located in the second region).

At this time, the voltage VA is applied to the first portion of theselected word line WL0 after the voltage VK3 is applied. Therefore, inthe first portion of the selected word line WL0, it takes some timeuntil stabilization at the voltage VA necessary for the reading occurs.However, since the columns of the first region in which the firstportion of the selected word line WL0 is located are non-selected, aproblem does not occur in the read operation in this example.

Subsequently, at time T44, the CG driver 42_0 supplies the voltage VK2to the selected word line WL0. Thus, the voltage VK2 is applied to thefirst portion of the selected word line WL0. In accordance with thevoltage VK2, the voltage VC is applied to the second portion of theselected word line WL0 without delay (that is, faster than when only VCis supplied to the first portion).

Thereafter, at time T45, the CG driver 42_0 supplies the voltage VC tothe selected word line WL0. Thus, the voltage VC is applied to the firstportion of the selected word line WL0. Then, reading is performed inaccordance with the voltage VC of the memory cell transistor MT0connected to the selected word line WL0 and connected to the selectedbit lines BL8 to BL15 (located in the second region).

At this time, the voltage VC is applied to the first portion of theselected word line WL0 after the voltage VK2 has been applied.Therefore, in the first portion of the selected word line WL0, it takessome time until stabilization at the voltage VC necessary for thereading occurs. However, as was the case at the time of reading inaccordance with the voltage VA, a problem does not occur in the readoperation in this example.

Thereafter, at time T46, the various voltages are returned to voltageVSS. Thus, each transistor is turned off and the read operation ends.

Advantages of Third Embodiment

In the third embodiment, the refresh operation is performed at thestarting of the read operation. During the time of discharging of theselected word lines WL after the refresh operation, the voltages to besupplied to the selected word lines WL are appropriately controlled infor the selection of the columns of the first region or the selection ofthe columns of the second region. Thus, even when the refresh operationis performed, the read voltages can still be applied rapidly to thefirst or second portion of the selected word lines WL, and thus it ispossible to achieve a shortening of a read time.

Fourth Embodiment

A semiconductor storage device according to a fourth embodiment will bedescribed with reference to FIG. 17. The fourth embodiment is amodification example of the third embodiment. Reading in accordance withthe voltage VC and reading in accordance with the voltage VA areperformed in sequence after the refresh operation. That is, the order ofthe reading (voltage C level first, then voltage A level second) is inreverse in this fourth embodiment as compared to the third embodiment(voltage A level first, then voltage C level second).

In the fourth embodiment, differences from the third embodiment will bemainly described and similarities will not be described.

Read Operation of Fourth Embodiment

Hereinafter, a read operation according to the fourth embodiment will bedescribed with reference to FIG. 17.

First, a timing chart in the case of selection of the columns (the bitlines BL0 to BL7) of the first region in the read operation will bedescribed with reference to FIG. 17. FIG. 17 illustrates an example inwhich the reading in accordance with the voltage VC and the reading inaccordance with the voltage VA are sequentially performed in order afterthe refresh operation is performed.

As illustrated in FIG. 17, at time T51 and time T52, the refreshoperation is performed as in the third embodiment.

Subsequently, at time T52, the CG driver 42_0 supplies the voltage VC tothe selected word line WL0. Thus, the voltage VC is applied to the firstportion of the selected word line WL0. Thus, reading is performed inaccordance with the voltage VC of the memory cell transistor MT0connected to the selected word line WL0 and connected to the selectedbit lines BL0 to BL7 (located in the first region).

At this time, a voltage greater than the voltage VC is being applied tothe second portion of the selected word line WL0. In other words, thesecond portion of the selected word line WL0 does not reach the voltageVC necessary for the reading due to long-distance delay. However, sincethe columns of the second region in which the second portion of theselected word line WL0 is located are non-selected, a problem does notoccur in the read operation in this example.

Subsequently, at time 154, the CG driver 42_0 supplies the voltage VA tothe selected word line WL0. Thus, the voltage VA is applied to the firstportion of the selected word line WL0. Then, reading is performed inaccordance with the voltage VA of the memory cell transistor MT0connected to the selected word line WL0 and connected to the selectedbit lines BL0 to BL7 (located in the first region).

At this time, a voltage greater than the voltage VA is being applied tothe second portion of the selected word line WL0. In other words, thesecond portion of the selected word line WL0 does not reach the voltageVA necessary for the reading due to long-distance delay. However, as atthe time of the reading in accordance with the voltage VC, a problemdoes not occur in the read operation in this example.

Thereafter, at time T56, the various voltages are returned to voltageVSS. Thus, each transistor is turned off and the read operation ends.

Next, a timing chart in the case of selection of the columns (the bitlines BL8 to BL15) of the second region in the read operation will bedescribed with reference to FIG. 17.

As illustrated in FIG. 17, at time T51 to time T52, the refreshoperation is performed as in the case of selection of the columns of thefirst region.

Subsequently, at time T52, the CG driver 42_0 supplies a voltage VK4 tothe selected word line WL0. Thus, the voltage VK4 (where VK4<VC) isapplied to the first portion of the selected word line WL0. Inaccordance with the voltage VK4, the voltage VC is, in effect, appliedto the second portion of the selected word line WL0 without delay(faster than when VC is supplied).

Thereafter, at time T53, the CG driver 42_0 supplies the voltage VC tothe selected word line WL0. Thus, the voltage VC is applied to the firstportion of the selected word line WL0. Then, reading is performed inaccordance with the voltage VC of the memory cell transistor MT0connected to the selected word line WL0 and connected to the selectedbit lines BL8 to BL15 (located in the second region).

At this time, the voltage VC is applied to the first portion of theselected word line WL0 after the voltage VK4 has been applied.Therefore, it takes some time until stabilization at the voltage VCnecessary for the reading occurs in in the first portion of the selectedword line WL0. However, since the columns of the first region in whichthe first portion of the selected word line WL0 is located arenon-selected, a problem does not occur in the read operation in thisexample.

Subsequently, at time T54, the CG driver 42_0 supplies a voltage VK5(where VK5<VA) to the selected word line WL0. Thus, the voltage VK5 isapplied to the first portion of the selected word line WL0. Inaccordance with the voltage VK5, the voltage VA is applied to the secondportion of the selected word line WL0 without delay (at least fasterthan when just voltage VA is supplied).

Thereafter, at time T55, the CG driver 42_0 supplies the voltage VA tothe selected word line WL0. Thus, the voltage VA is applied to the firstportion of the selected word line WL0. Then, reading is performed inaccordance with the voltage VA of the memory cell transistor MT0connected to the selected word line WL0 and connected to the selectedbit lines BL8 to BL15 (located in the second region).

At this time, the voltage VA is applied to the first portion of theselected word line WL0 after the voltage VK5 is applied. Therefore, ittakes some time until stabilization at the voltage VA necessary for thereading occurs in the first portion of the selected word line WL0.However, as at the time of reading in accordance with the voltage VC, aproblem does not occur in the read operation in this example.

Thereafter, at time T56, various voltages are voltages VSS. Thus, eachtransistor is turned off and the read operation ends.

Advantages of Fourth Embodiment

In the fourth embodiment, the reading in accordance with the voltage VCand the reading in accordance with the voltage VA are performed insequence after the refresh operation has been performed. That is, theorder of read voltages goes in the direction of decreasing voltage leveland the reading is performed in this order. At the time of dischargingof the selected word lines WL after the refresh operation and the timeof discharging after the reading in accordance with the voltage VC, thevoltages to be supplied to the selected word lines WL are appropriatelycontrolled in the case of selection of the columns of the first regionand the case of selection of the columns of the second region. Thus,even when the refresh operation is performed, and the read voltages aredropped and the reading is performed, the read voltages can be appliedrapidly to the first or second portion of the selected word lines WL,and thus it is possible to achieve shortening of a read time.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A semiconductor storage device, comprising: afirst memory cell electrically connected to a first bit line and a firstword line; a second memory cell electrically connected to a second bitline and the first word line; and a first circuit configured to supplyvoltages to the first word line, wherein during a reading operation toread a page of memory cells including the first memory cell and thesecond memory cell, while the first memory cell is selected as a readtarget during a first time period, the first circuit supplies: a firstvoltage to the first word line, a second voltage less than the firstvoltage to the first word line after supplying the first voltage, and athird voltage greater than the second voltage to the first word lineafter supplying the second voltage; and during the reading operation toread the page of memory cells including the first memory cell and thesecond memory cell, while the second memory cell is selected as the readtarget during a second time period that is different from the first timeperiod, the first circuit supplies: the first voltage to the first wordline, a fourth voltage less than the second voltage to the first wordline after supplying the first voltage, the second voltage to the firstword line after supplying the fourth voltage, and a fifth voltagegreater than the third voltage to the first word line after supplyingthe second voltage.
 2. The semiconductor storage device according toclaim 1, wherein a distance from the first circuit to the first memorycell is shorter than a distance from the first circuit to the secondmemory cell.
 3. The semiconductor storage device according to claim 1,wherein during the reading operation to read the page of the memorycells, while the second memory cell is selected as the read targetduring the second time period, the first circuit supplies the secondvoltage to the first word line directly after supplying the fourthvoltage.
 4. The semiconductor storage device according to claim 3,wherein during the reading operation to read the page of the memorycells, while the second memory cell is selected as the read targetduring the second time period, the first circuit supplies the thirdvoltage to the first word line directly after supplying the fifthvoltage.
 5. The semiconductor storage device according to claim 4,wherein during the reading operation to read the page of the memorycells, while the first memory cell is selected as the read target duringthe first time period, the first circuit supplies: the second voltage tothe first word line directly after supplying the first voltage, and thethird voltage to the first word line directly after supplying the secondvoltage; and during the reading operation to read the page of the memorycells, while the second memory cell is selected as the read targetduring the second time period, the first circuit supplies: the fourthvoltage to the first word line directly after supplying the firstvoltage, and the fifth voltage to the first word line directly aftersupplying the second voltage.
 6. The semiconductor storage deviceaccording to claim 1, further comprising: a third memory cellelectrically connected to a third bit line and the first word line, thethird bit line being between the first bit line and the second bit line;and a fourth memory cell electrically connected to a fourth bit line andthe first word line, the second bit line being between the third bitline and the fourth bit line, wherein during the reading operation toread the page of the memory cells, while the first memory cell isselected as the read target during the first time period, the firstcircuit supplies: a sixth voltage to the first bit line, and a seventhvoltage to the third bit line, the second bit line and the fourth bitline; and during the reading operation to read the page of the memorycells, while the second memory cell is selected as the read targetduring the second time period, the first circuit supplies: the sixthvoltage to the second bit line, and the seventh voltage to the first bitline, the third bit line and the fourth bit line.
 7. The semiconductorstorage device according to claim 1, wherein the first and second bitlines are adjacent.
 8. The semiconductor storage device according toclaim 1, wherein the first memory cell is between the first circuit andthe second memory cell along the first word line.
 9. A semiconductorstorage device, comprising: a first memory cell electrically connectedto a first bit line and a first word line; a second memory cellelectrically connected to a second bit line and the first word line; anda first circuit configured to supply voltages to the first word line,wherein during a reading operation to read a page of memory cellsincluding the first memory cell and the second memory cell, while thefirst memory cell is selected as a read target during a first timeperiod, the first circuit supplies: a first voltage to the first wordline, a second voltage less than the first voltage to the first wordline after supplying the first voltage, and a third voltage less thanthe second voltage to the first word line directly after supplying thesecond voltage; and during the reading operation to read the page ofmemory cells including the first memory cell and the second memory cell,while the second memory cell is selected as the read target during asecond time period that is different from the first time period, thefirst circuit supplies: the first voltage to the first word line, afourth voltage less than the second voltage to the first word linedirectly after supplying the first voltage, the second voltage to thefirst word line directly after supplying the fourth voltage, and a fifthvoltage less than the third voltage to the first word line directlyafter supplying the second voltage.
 10. The semiconductor storage deviceaccording to claim 9, wherein a distance from the first circuit to thefirst memory cell is shorter than a distance from the first circuit tothe second memory cell.
 11. The semiconductor storage device accordingto claim 9, wherein during the reading operation to read the page of thememory cells, while the second memory cell is selected as the readtarget during the second time period, the first circuit supplies thesecond voltage to the first word line directly after supplying thefourth voltage.
 12. The semiconductor storage device according to claim11, wherein during the reading operation to read the page of the memorycells, while the second memory cell is selected as the read targetduring the second time period, the first circuit supplies the thirdvoltage to the first word line directly after supplying the fifthvoltage.
 13. The semiconductor storage device according to claim 12,wherein during the reading operation to read the page of the memorycells, while the first memory cell is selected as the read target duringthe first time period, the first circuit supplies: the second voltage tothe first word line directly after supplying the first voltage, and thethird voltage to the first word line directly after supplying the secondvoltage; and during the reading operation to read the page of the memorycells, while the second memory cell is selected as the read targetduring the second time period, the first circuit supplies: the fourthvoltage to the first word line directly after supplying the firstvoltage, and the fifth voltage to the first word line directly aftersupplying the second voltage.
 14. The semiconductor storage deviceaccording to claim 9, further comprising: a third memory cellelectrically connected to a third bit line and the first word line, thethird bit line being between the first bit line and the second bit line;and a fourth memory cell electrically connected to a fourth bit line andthe first word line, the second bit line being between the third bitline and the fourth bit line, wherein during the reading operation toread the page of the memory cells, while the first memory cell isselected as the read target during the first time period, the firstcircuit supplies: a sixth voltage to the first bit line, and a seventhvoltage to the third bit line, the second bit line and the fourth bitline, and during the reading operation to read the page of the memorycells, while the second memory cell is selected as the read targetduring the second time period, the first circuit supplies: the sixthvoltage to the second bit line, and the seventh voltage to the first bitline, the third bit line and the fourth bit line.
 15. The semiconductorstorage device according to claim 9, wherein the first and second bitlines are adjacent.
 16. The semiconductor storage device according toclaim 9, wherein the first memory cell is between the first circuit andthe second memory cell along the first word line.